The present invention relates generally to data communications, and more particularly, to a system and method for indicating an efficient information rate during a data format conversion.
Data communications employs many different data communications protocols to transmit data from one point to another in various networks. Oftentimes, a data link between two endpoints requires the use of more than one type of protocol, where protocol conversion devices are employed to effect the conversion. An example would be the use of frame relay networks and asynchronous transfer mode (ATM) networks in a single data link.
To explain further, frame relay format transmits data in the form of data frames or packets that will vary in length and include a data payload of variable length, anywhere from 1 byte to 4 kilobytes. ATM format employs 53 byte cells that carry a data payload of a fixed 48 bytes per cell. A frame relay device typically provides a specific committed information rate (CIR) for an end user that is generally a rate of information exchange based upon the type of data payloads transmitted.
ATM network service providers also configure their networks to guarantee end users with a specific rate of information exchange known as a sustained cell rate (SCR). The sustained cell rate refers to the number of ATM cells that may be transmitted per second carrying the end user""s data in a continuous manner.
In some cases, an end user may employ devices that use a frame relay protocol, but may wish to link up to a ATM network to achieve high speed communication with a remote location linked to the ATM network. As such, the end user may employ a frame relay/ATM conversion device to convert the data frames into ATM cells. In these situations, the end user often pays for and receives a specific SCR for the ATM connection. For a given SCR, there is a particular calculated CIR that can be accommodated. Typically the end user receives periodic reports from the ATM service provider as to the amount of the end user""s data transferred at what data rates via the ATM network. By comparing the report to the calculated CIR, the user can determine how much of their data was transferred at a data rate above and below the calculated CIR. Any such data transferred above the calculated CIR is subject to being dropped since it exceeds the contracted data rate. Consequently, it is in the end user""s interest to ensure that the contracted SCR is high enough to prevent such a loss of data.
However, due to the conversion from frame relay into ATM, the calculated CIR is not always an accurate value due to the fact that an estimated value for the data packet size is used in the calculation of the CIR at a given SCR. The inaccuracy of this estimated value may result in an inaccurately calculated CIR.
In light of the forgoing, the present invention provides a system and method for determining an efficient and accurate committed information rate (CIR) for a frame relay data communications device to facilitate the conversion of frame relay data packets into asynchronous transfer mode (ATM) data cells. In one embodiment, the present system includes a processor coupled to a local interface, a memory coupled to the local interface, an adaptive CIR logic stored in the memory, the adaptive CIR logic being executed by the processor, the adaptive CIR logic including: sample identification logic to identify at least one sample group of a number of data packets transmitted across a data communications link, the data packets having a variable length and the data cells having a fixed length, modeling logic to adapt a modeled packet size of the frame relay data packets transmitted across the data communications link based upon the data packets in the sample group, and, logic to calculate an efficient committed information rate based upon the modeled packet size. The adaptive CIR logic may also be implemented in terms of a dedicated logical circuit or by a combination of a processor circuit and dedicated logical circuits.
In another embodiment, the method of the present invention is provided for determining an efficient committed information rate (CIR) for a frame relay data communications device to facilitate the conversion of frame relay data packets into asynchronous transfer mode (ATM) data cells, comprising the steps of: identifying at least one sample group of a number of data packets transmitted across a data communications link, the data packets having a variable length and the data cells having a fixed length; adapting a modeled packet size of the frame relay data packets transmitted across the data communications link based upon the data packets in the sample group; and, calculating the efficient committed information rate based upon the modeled packet size.
The present invention provides a distinct advantage in that a more accurate and efficient CIR is calculated on the frame relay side of a frame relay/ATM conversion. An accurately determined CIR allows the user who employs frame relay to know what information rates to expect as a result of a contracted for ATM service. Thus the frame relay user can better decide if they need to contract for a smaller or greater SCR from their ATM service provider.